1. Field of the Invention
This invention relates to a reference solution utilized at the time of measuring the activity of a particular ion in an aqueous solution, particularly a biological body fluid such as blood, which is superior in prevention of putrefaction.
2. Background of the Invention
When activity of a particular ion in an aqueous solution, especially in a biological body fluid such as blood is measured by the differential method using a ion-selective electrodes, a reference solution is usually employed. This reference solution is generally composed of an electrolyte such as sodium chloride, ammonium chloride, ammonium nitrate, potassium chloride, sodium hydrogen carbonate, sodium dihydrogen phosphate or potassium dihydrogen phosphate, a buffering agent, a water-soluble polymer, an antiseptic, etc. The antiseptic is added in order to prevent generation of fungi and putrefaction of the reference solution, and salicylic acid, thymol, benzoic acid, sodium azide or the like has been employed as the antiseptic. However, heretofore, even in the presence of such an antiseptic, fungi were often generated in a relatively short preservation period, and they putrefied the reference solution. Besides, the potential (difference) generated in an ion-selective electrode was often influenced by the antiseptic added.